Thermoformed autovehicles interiors are generally obtained from sheets comprising a support material and an external covering layer for aesthetic purposes. According to a widely known and used technique, the external covering (known as "imitation leather") is produced separately and thereafter joined to the support previously heated in a press. The press also provides for the shaping of the panel into the required form.
The support material is generally a polyolefin resin with a vegetable filler comprising for the most part wood powder. The imitation leather is generally in PVC and comprises a layer of cotton fabric or other textile material which acts as a mechanical bonding means for the polyolefin support.
This technique has several of drawbacks. In the first place, the cost and weight of the traditional imitation leather in PVC are both quite high. A second problem arises from the costs of the process, which requires many steps--some of which are particularly long--such as the cutting of the imitation leather and its positioning on the support plate. Further problems derive from the anisotropy of the panel as produced, from the fact that to recycle the waste or the panel at the end of its life it is necessary to remove the imitation leather (PVC) from the support layer (PP), and problems arise from the mechanical and hand (touch) characteristics of the product.
It has been proposed to produce the panels and the vehicle interior elements by co-injecting the support material and the external imitation leather material. This solution resolves many of the preceding problems but is suited to some types of panel only. The European Patent Application no. 0668142 discloses a method according to which sheets formed from a support layer and two external covering layers are co-extruded; these sheets are then thermoformed to give trim panels for cars, packing containers and the like. The support comprises polyolefin and an organic filler, particularly cellulose fibers, and the covering layers comprise polyolefin and inorganic fillers such as talc and carbonate. Panels of this type apparently present acceptable mechanical characteristics, but aesthetic and hand characteristics are completely insufficient.